The invention concerns a separation device for separation of blood into its components within the framework of in-vivo blood processing, with a separator which has a intake line with a pump whose flow can be adjusted to supply the blood to be separated and discharge lines for the separated output of at least the erythrocyte fraction and the cell-poor plasma, as well as a return line via which at least one component can be returned to the donor/patient, and with a control arrangement to which a signal representing the hematocrit value of the incoming blood (hematocrit signal) is sent.
Such a separation device, which is used in particular during intraoperative blood processing, is known from U.S. Pat. No. 3,957,197. In the known case, the hematocrit signal is connected to a regulating step with which the hematocrit value of the whole blood (proportion of erythrocytes to the volume of the peripheral blood in vol.-%) is kept at a constant value. For this the hematocrit value of the whole blood is measured in the intake line (actual value) and compared to a desired value. If the hematocrit value measured is higher than the desired value, it is adjusted to the preset value by addition into the intake of a separated fraction from the appropriate discharge lines via a precision dosing pump. Thus, the relationship of plasma flow to erythrocyte flow can be adjusted to a constant defined value and an improvement in the efficiency of the separation device with regard to cell collection in treatment of relatively large amounts of blood can thus be obtained.
Devices with improved efficiency in blood collection and treatment of larger amounts of blood are also presented in DE 34 10 286 A1 (identical to EP 0 155 684 A2). DE 34 10 286 A1 describes a device whereby the hematocrit of whole blood delivered to a centrifuge is adjusted in the desired low range (e.g., 25%) by means of plasma return, and whereby the centrifuge accomplishes optimum separation efficiency. The centrifuge separates the blood the most rapidly at an input value of 25% erythrocytes in the whole blood and with constant input flow and constant speed; the final value of the hematocrit of the cell concentrate, i.e., the erythrocyte fraction (e.g., 70%) is obtained the most rapidly. For this reason, plasma obtained through centrifuging is added and the blood thus thinned.
An analogous prior art device with control of the hematocrit value of the whole blood delivered at a constant value was disclosed in the article by B. J. Van Wie and S. S. Sofer: "The effect of recycle on the continuous centrifugal processing of blood cells", The International Journal of Artificial Organs, Vol. 8, No. 1, 1985, pp. 43-48.
However, in certain medical applications, in particular in intraoperative blood processing, one must assume widely scattered (i.e., extremely varied) high hematocrit values for the whole blood supplied to a separation device, which values cannot be influenced by control technology. The known devices cannot be used in those cases. However, the hematocrit value of the incoming blood plays a significant role relative to the sedimentation of cellular blood components in a centrifuge, since sedimentation is a function of the hematocrit value in addition to the size, density, and shape of the blood cells. Consequently, incoming blood with different hematocrit values is separated into cell fractions of differing concentrations if it is processed for the same length of time in a centrifuge. This relationship between the hematocrit value of the blood (=Hk blood in %) and the hematocrit value of the erythrocyte fraction (HkEk in %) with a constant blood flow of 120 ml/min is depicted in FIG. 1. The HkEK decreases as Hk blood increases.
The relationships are similar with other separation devices, in particular filtration systems which can also be used.
The dependency depicted in FIG. 1 is without particular significance in those typical cases wherein adequate processing periods in the centrifuges can be implemented and wherein possibly even relatively poor separation efficiency is acceptable. Furthermore, on average the incoming hematocrit value of the donor blood has only slight fluctuations, so that the associated effects are also negligible in such cases.
However, the situation is different particularly in the area of intraoperative autotransfusion, in particular during plasma separation and irrigation processes. There, the hematocrit value plays a very critical role. Intraoperative blood suctioned in the operative field and temporarily held in a collection container has quite variable hematocrit values depending on the type of operation, the hematocrit value of the patient, the amount of irrigation solution used in the operative field, the amount of volume expander infused, patient blood loss, the amount of anticoagulant added, or the amount of fluid flowing in, for example from the tissue. These are in the range from ten to forty percent and can vary arbitrarily during an operation. In contrast, the normal values are forty-six percent by volume for men and forty for women. The processing methods currently used do not take these fluctuations in the hematocrit value into account and usually operate with constant, preset rates of delivery of blood into the centrifuge. This leads to the following consequences:
1. The hematocrit value of the erythrocyte concentrate produced is subject to large fluctuations. PA1 2. The plasma washout rate, which is defined by the volume relationship of the residual plasma to be washed out remaining in the cell concentrate to the irrigation solution added, is subject to significant fluctuations. PA1 3. The sedimentation capacity of the separation device cannot be optimally utilized.
Furthermore, a constant hematocrit value of the erythrocyte concentrate produced is imperative for the exact documentation of the retransfused erythrocyte quantity by the retransfused erythrocyte concentrate volume. It is desirable to work with the highest possible blood processing speed and to work with a constant washout rate.
The object of the invention is to improve the separation device described in the introduction such that despite the widely fluctuating hematocrit value of the incoming blood a constant hematocrit value of the prepared cell concentrate can be obtained. Additional objectives are a constant washout rate and optimum utilization of the sedimentation performance of the separation device used to optimize blood throughput.